Fetal Nociception: The Unconscious Experience of Pain

by Jennifer Cortes

Since 2010, 13 states have enacted a 20-week abortion ban. With all eyes on the 2016 presidential candidates, it is no surprise that Wisconsin Governor Scott Walker made headlines when he signed a 20-week abortion ban into law in early July. Commenting on the bill, Walker said “At five months, that’s the time when that unborn child can feel pain. When an unborn child can feel pain, we should be protecting that child.”

A group of gynecologists responded to the bill by writing Walker a letter in which they mentioned that it is a "thoroughly debunked fallacy that a 20-week fetus…can feel pain.” All politics and vague research references aside, what really is known about the development and experience (or lack thereof) of pain in the fetus?

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The Committee on Taxonomy of the International Association for the Study of Pain provides a commonly used definition of pain: “An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage…activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state.”

Essentially, this means that pain involves both a physiological detection of a potentially harmful stimulus (i.e. pain pathways must be present and functional) and also an awareness of the stimulus associated with disagreeable feelings (i.e. consciousness is required). To appreciate this distinction, consider what happens when you touch a hot pan – you reflexively yank your hand away before you experience the feeling of pain. Thus, your reaction and the sensation of pain are related but distinct.  

The point of contention does not lie in the nociceptors (pain receptors), which appear around the fetus’s mouth at the seventh week of gestation (or equivalently, the fifth week after fertilization). By the 20th week, nociceptors are present throughout the whole body. Nerves connecting these nociceptors to the thalamus (the region of the brain involved in pain implication) finish developing at 20 weeks.

In addition, research conducted on fetal behavioral responses reveals that activity is induced in the fetus’s nociceptive pathways when a noxious stimulus is applied. This behavioral response is frequently mentioned in articles that conclude that the fetus feels pain, as well as in articles that reach the opposite conclusion. When an intrauterine blood sample is taken, for instance, the fetus responds by moving away from the needle and stress hormone levels increase. Even during invasive surgery, fetal surgeons must sedate the fetus so that it does not respond by thrashing. This strongly indicates that the fetus not only possesses pain pathways, but that these pathways can be activated.

Although the presence and functional ability of pain tracks are unarguable, awareness in the fetus is not so easily addressed, partly due to the inability to test this phenomenon and the difficulty in ruling out conflicts of interest in the most highly cited journal articles on the topic. The two papers that argue whether a fetus experiences “a state of true wakefulness in utero” are “Fetal Pain: A Systematic Multidisciplinary Review of the Evidence” published in the Journal of the American Medical Association (JAMA) and “Fetal Awareness: Review of Research and Recommendations for Practice” published by the Royal College of Obstetricians and Gynaecologists (RCOG).

It must be noted that one of the authors in the JAMA article was an abortion provider and another was a lawyer at NARAL – one of the nation’s leading pro-choice organizations. Similarly, the RCOG also has a conflict of interest as it “views induced abortions as a healthcare need as well as an important public health intervention.” Thus, while bias in their conclusions cannot be disregarded, they are still worth discussing. Both articles argue that connections between the thalamus and cerebral cortex are essential to an awareness of pain but do not appear in the fetus until at least 23 weeks of gestation.

In contradiction, Bjorn Merker – a neuroscientist who primarily studies the brain’s mechanism of consciousness – concludes in his paper “Consciousness without a Cerebral Cortex: A Challenge for Neuroscience and Medicine” that the function of the consciousness is one that precedes the evolutionary invention of the neocortex, meaning that rather than necessitating the cortex, consciousness might only rely on the upper brainstem. Merker discusses children with hydranencephaly, a condition in which a substantial portion of the cortex is missing. Despite their lack of cortical tissue – analogous to a fetus – Merker points out that these children still have appropriate emotional reactions: smiling, laughing and crying.

An additional claim made by the RCOG article is that the fetus is “sedated by the physical environment of the womb and usually does not awaken before birth” based on sleep-like EEG patterns observed in compared lamb fetuses. Doctors on Fetal Pain – a collaboration of physicians who believe there is substantial scientific evidence of fetal pain – contradict this position by pointing to the response of fetuses to intrauterine needles and procedure. However, as previously mentioned, this could potentially be reflex mediated and not involve higher brain areas.

Overall, research has not yet come to a conclusive answer on the question of awareness in a fetus – nociception is unarguable, but pain awareness is debatable. Perhaps one day science and technology will allow us to more fully understand what occurs in the fetal brain and the state of their consciousness. Even then, it might be impossible to know with certainty if a fetus is aware, and we may only ever have speculation.